1. Field of the Invention
The present invention relates to a steering tube sleeve and stem tube assembly for cycles, particularly lightweight bicycles for recreational riding, racing, or off-road uses.
Since rider safety and reduction of weight is of extreme importance in human-powered cycles such as bicycles, increasing use has been made of strong lightweight composite tubular structures instead of aluminum or steel tubular frame parts and handlebars. Such composites, such as carbon reinforced resins, are easily damaged and the need therefore exists for a steering tube sleeve and stem assembly which can be readily attached to the cycle steering tube and which can be removed therefrom for re-positioning or replacement without damaging the steering tube, particularly when the steering tube is made of composites.
2. Prior Art
U.S. Pat. No. 5,193,930 issued Mar. 16, 1993 to Chi discloses a coupling for securing a handlebar stem to the upper end of a front fork steering tube. Spaced lugs punched out from and extending from a tube sleeve are bolted together and are enclosed by a horizontally extending stem tube which is welded to the sleeve. Access to the clamping bolt is through a hole in the side wall of the stem tube.
Substantial bending and torsional stresses are placed on the connection of a handlebar stem to a steering tube as is well known. Failures occur when structural weaknesses are created by excessive machining of sleeves as by punching lugs therefrom and when welded joints are of insufficient length to adequately withstand the forces applied thereto.